In digital image print systems, physical alignments, component tolerances, wear and component age can influence the macro-uniformity with which colorants, such as inks and toners, are laid down across the surface of print media. Detection of such print defects helps device operators and system designers ensure the continued production of uniform quality images throughout the life of a document reproduction device. Although some defects impacting image quality may not be entirely visible to the unaided eye, these defects nonetheless indicate that one or more aspects of the print device are no longer performing within acceptable parameters and/or defined tolerances.
Banding is one image quality defect which can occur in complex digital document reproduction system architectures. Banding defects are often observed as periodic variations in printing intensity along the printing direction of the digital document reproduction system. Banding defects are visually objectionable image quality artifacts caused by mechanical or electronic defects in the print engine used to render the output image. Banding defects can also “beat” with other frequency components in the print device, such as halftones, to cause objectionable secondary banding defects.
Deterioration in the performance or function of components of a document reproduction system may induce banding defects that are able to be observed in the output of such systems. Often, defects of various components in the document reproduction system will exhibit banding defects in the output of such systems that exhibit a particular frequency. Identification of an increase in amplitude at such particular frequencies in the printed output of a document reproduction system indicates that the component, such as an internal part or subsystem, requires service or replacement. The output of a document reproduction system can be analyzed to identify an increase in amplitude at particular frequencies of banding defects. The identification of a banding defect with significant amplitude at a particular frequency in the output of a document reproduction system indicates that the component or subsystem associated with that frequency requires service or replacement.
In order to maintain a quality of output for a document reproduction system, it is advantageous to monitor the system's banding performance to detect banding defects prior to the amplitudes of those banding defects reaching an unacceptable level. Some systems cause the document reproduction system to print pre-designed test targets that are then analyzed to detect banding defects. Such test targets can be designed to cause outputs to be printed that are highly sensitive to low amplitude banding defects induced by the document reproduction system. However, test-target printing in a production document reproduction system interrupts regular print/copy jobs, reduces job throughput, and wastes valuable time and resources.
Accordingly, what is needed in this art are increasingly sophisticated methods to detect and analyze banding defects on user document images to improve real-time image quality trend analysis in digital imaging systems.